Reinforcing method and reinforcing structure for steel structure and elastic layer forming material for reinforcing steel structure

ABSTRACT

A reinforcing method and structure for a steel structure and an elastic layer forming material for reinforcing a steel structure are provided that can prevent a reinforcing effect from being lowered by direct sunlight, can obtain a sufficient reinforcing effect, and can prevent a fiber sheet from being peeled away from a steel structure surface before the fiber sheet is torn. The reinforcing method for a steel structure, in which a fiber sheet including reinforcing fibers is bonded to a surface of the steel structure to integrate the fiber sheet with the steel structure, includes (a) a step of applying and hardening a polyurea resin putty to the surface of the steel structure to form an elastic layer, and (b) a step of bonding the fiber sheet to the surface of the steel structure having the elastic layer formed thereon with an adhesive agent.

TECHNICAL FIELD

The present invention relates a reinforcing method and a reinforcingstructure for a steel structure and an elastic layer forming materialfor reinforcing a steel structure that repair and reinforce (to besimply referred to as “reinforce” hereinafter) steel structures of abridge, a pier, a chimney, furthermore, a ship, a vehicle, and anaircraft by using a sheet-like reinforcing-fiber-containing material (tobe referred to as a “fiber sheet” hereinafter) including continuousreinforcing fibers.

BACKGROUND ART

In recent years, as a reinforcing method for an existing or new steelstructure, a continuous fiber sheet bonding method such as acarbon-fiber sheet bonding method or an aramid fiber sheet bondingmethod that attaches or winds a continuous reinforcing-fiber sheet suchas a carbon fiber sheet or an aramid fiber sheet to the surface of thesteel structure is given. A method in which a fiber sheet obtained byimpregnating an unhardened matrix resin in continuous fiber bundles isbonded to adhere to a steel structure and then hardened is also given.

Furthermore, in order to omit the impregnation of a resin on site, anFRP plate bonding-reinforcing method in which a factory-produced FRPplate having a thickness of 1 to 2 mm and a width of about 5 cm isbonded to a steel structure by using a putty-like adhesive resin is alsodeveloped.

A steel structure reinforced by the above methods can obtain an enhancedreinforcing effect by a fiber sheet as long as the fiber sheet isintegrally bonded to the steel structure. However, when the steelstructure is deformed with a load, a desired object cannot be achievedwhen the fiber sheet is peeled away from the steel structure surfacebefore the fiber sheet is broken.

Thus, Patent Document 1 discloses a method in which a buffer materiallayer is formed on the surface of a steel structure and, thereafter, afiber sheet is bonded thereto with an adhesive agent to reinforce thesteel structure. It is disclosed that, as the buffer material layer, aresin such as a thermosetting resin or a thermoplastic resin can beused. In addition, it is disclosed that a tensile elasticity modulus at23° C. when the resin is singularly hardened is 0.1 to 50 N/mm².

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Patent Publication No. 3553865

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, as a result of an experimental research by the presentinventors, it was newly found that a problem in which a fiber sheet ispeeled away from a steel structure surface when the steel structure isreinforced, unlike in a case in which a concrete structure is reinforcedwith a fiber sheet, is considerably influenced by a temperature of thesteel structure surface. Thus, when the steel structure is to bereinforced with a fiber sheet, the temperature of the steel structuresurface must be sufficiently considered. The steel structure (steelproduct) has elongation caused by a change in temperature and deflectioncaused by vehicle traffic or the like that are larger than those of aconcrete structure. For this reason, when a rigid continuous fiber sheetis bonded to the steel structure, it is concerned that the fiber sheetis peeled away from the structure at an end of the fiber sheet.

And also, it is known that a steel structure, for example, in thiscountry, has a surface temperature that increases to a temperature ofabout 60° C. due to direct sunlight in midsummer. For this reason, whenan adhesive agent or the like used in reinforcement by a fiber sheetaccording to a conventional specification is used, the adhesive agent issoftened by the high surface temperature. In some case, it was foundthat a necessary reinforcing effect cannot be obtained.

In the reinforcing method according to Patent Document 1, a tensileelasticity modulus of a resin forming a buffer material layer is low.When the steel structure is reinforced with a rigid continuous fibersheet or the like, the buffer material layer may not be able to transmitstress to be originally transmitted to the fiber sheet. Morespecifically, in this case, the fiber sheet is ineffective to make itimpossible to reinforce the steel structure.

It is an object of the present invention to provide a reinforcing methodand a reinforcing structure for a steel structure and an elastic layerforming material for reinforcing a steel structure in which, when asteel structure is reinforced with a fiber sheet, a reinforcing effectby the fiber sheet is prevented from being eliminated by sunlightirradiation or the like, a sufficient reinforcing effect can beobtained, and the fiber sheet is prevented from being peeled away fromthe steel structure surface before the fiber sheet is torn.

Means to Solve the Problem

According to the present invention, the object is achieved by thereinforcing method and the reinforcing structure for a steel structureand an elastic layer forming material for reinforcing a steel structure.In short, according to a first invention, there is provided areinforcing method for a steel structure in which a fiber sheetcontaining reinforcing fibers is bonded to the surface of a steelstructure to integrate the steel structure and the fiber sheet with eachother and which comprises the steps of:

(a) applying a polyurea resin putty to a surface of the steel structureand hardening the polyurea resin putty to form an elastic layer; and

(b) bonding the fiber sheet to the surface of the steel structure havingthe elastic layer formed thereon with an adhesive agent.

According to an embodiment of the first invention, the adhesive agentused in the step (b) has a glass transition temperature that is adjustedsuch that a reinforcing effect can be maintained even at a hightemperature. For example, the adhesive agent has a glass transitiontemperature of 60° C. or more.

According to another embodiment of the first embodiment, a polyurearesin putty that forms the elastic layer in the step (a) contains a mainresin, a hardening agent, a filler, and an additive agent and has acomposition containing:

(i) the main resin: a prepolymer containing an isocyanate as a reactivecomponent and having residual terminal isocyanate the NCO weight percentof which is adjusted to 1 to 16 parts by weight is used;

(ii) the hardening agent: a hardening agent containing an aromatic amineas a main component is used, an equivalence ratio of NCO serving as themain resin to an amine being given by 1.0:0.55 to 0.99 parts by weight;

(iii) the filler: a filler contains silica powders, a thixotropic agent,and the like, and is arbitrarily compounded at 1 to 500 parts by weight;and

(iv) the additive agent: an additive agent contains a coloring agent, aviscosity modifier, an elasticizer, and the like, and is arbitrarilycompounded at 1 to 50 parts by weight.

According to another embodiment of the first invention, the adhesiveagent used in the step (b) is a room-temperature-setting epoxy resin, anepoxy acrylate resin, an acrylic resin, an MMA resin, a vinylesterresin, an unsaturated polyester resin, or a UV curable resin.Preferably, the adhesive agent is an epoxy resin adhesive agent. Theepoxy resin adhesive agent is provided by two components including amain resin and a hardening agent, and has a composition containing:

(i) the main agent: a main resin containing an epoxy resin as a maincomponent and a silane coupling agent or the like serving as an adhesionenhancing agent as needed is used; and

(ii) the hardening agent: a hardening agent contains amines as maincomponents, an equivalence ratio of an epoxy resin serving as the mainresin to amines of the hardening agent being 1:1.

According to still another embodiment of the first invention, prior toforming the elastic layer on the surface of the steel structure, themethod includes the step of performing surface preparation to thesurface of the steel structure and/or the step of applying a primer.

According to still another embodiment of the first invention, the fibersheet is a fiber sheet in which continuous reinforcing fibers arrangedin one direction are fixed with a strands fixing member. The fiber sheetis a fiber sheet in which a plurality of continuous fiber-reinforcedplastic strands each formed by impregnating the matrix resin in thereinforcing fibers and hardening the resin, are arranged in thelongitudinal direction in the form of a blind and fixed to each otherwith a strand fixing member. Alternatively, the fiber sheet is a fibersheet in which a resin is impregnated in continuous reinforcing fibersheets arranged in one direction and is hardened.

According to still another embodiment of the first invention, the fibersheets are laminated as a plurality of layers on the surface of thesteel structure and integrated with the steel structure.

According to a second invention, in the reinforcing method for a steelstructure described above, there is provided an elastic layer formingmaterial for reinforcing a steel structure configured by a polyurearesin putty for forming the elastic layer. The polyurea resin puttycontains a main resin, a hardening agent, a filler, and an additiveagent, and is characterized by including a composition containing:

(i) the main resin: a prepolymer containing isocyanate as a reactivecomponent and having residual terminal isocyanate the NCO weight percentof which is adjusted to 1 to 16 parts by weight is used;

(ii) the hardening agent: a hardening agent containing an aromatic amineas a main component is used, an equivalence ratio of NCO serving as themain resin to an amine being given by 1.0:0.55 to 0.99 parts by weight;

(iii) the filler: a filler contains silica powders, a thixotropic agent,and the like, the components being arbitrarily combined with each otherat 1 to 500 parts by weight; and

(iv) the additive agent: an additive agent contains a coloring agent, aviscosity modifier, an elasticizer, and the like, the components beingarbitrarily combined with each other at 1 to 50 parts by weight. Thepolyurea resin putty has a tensile elongation of 400% or more inhardening, a tensile strength of 8 N/mm² or more, and a tensile elasticmodulus of 60 N/mm² or more and 500 N/mm² or less.

According to a third invention, there is provided a reinforcingstructure for a steel structure characterized by including:

(a) an elastic layer formed by applying a polyurea resin putty on asurface of the steel structure; and

(b) a fiber sheet layer bonded to the surface of the steel structurehaving the elastic layer formed thereon with an adhesive agent andimpregnated with a resin.

According to one embodiment of the third invention, the elastic layerhas a tensile elongation of 400% or more in hardening, a tensilestrength of 8 N/mm² or more, and a tensile elasticity modulus of 60N/mm² or more and 500 N/mm² or less.

According to another embodiment of the third invention, the adhesiveagent has a glass transition temperature that is adjusted such that areinforcing effect can also be maintained even at a high temperature.For example, the adhesive agent has a glass transition temperature of60° C. or more.

In the third invention, preferably, the polyurea resin putty contains amain resin, a hardening agent, a filler, and an additive agent, and hasa composition containing:

(i) the main resin: a prepolymer containing isocyanate as a reactivecomponent and having residual terminal isocyanate the NCO weight percentof which is adjusted to 1 to 16 parts by weight is used;

(ii) the hardening agent: a hardening agent containing an aromatic amineas a main component is used, an equivalence ratio of NCO serving as themain resin to an amine being given by 1.0:0.55 to 0.99 parts by weight;

(iii) the filler: a filler contains silica powders, a thixotropic agent,and the like, the components being arbitrarily combined with each otherat 1 to 500 parts by weight; and

(iv) the additive agent: an additive agent contains a coloring agent, aviscosity modifier, an elasticizer, and the like, the components beingarbitrarily combined with each other at 1 to 50 parts by weight. As theadhesive agent, a room-temperature-setting epoxy resin, an epoxyacrylate resin, an acrylic resin, an MMA resin, a vinylester resin, anunsaturated polyester resin, or a UV curable resin is used. Preferably,the adhesive agent is an epoxy resin adhesive agent. The epoxy resinadhesive agent is provided by two components including a main resin anda hardening agent, and has a component containing:

(i) the main resin: a main resin containing an epoxy resin as a maincomponent and a silane coupling agent or the like serving as an adhesionenhancing agent as needed is used; and

(ii) the hardening agent: a hardening agent contains amines as maincomponents, an equivalence ratio of an epoxy resin serving as the mainresin to amines of the hardening agent being 1:1.

Effect of the Invention

According to a reinforcing method and a reinforcing structure for asteel structure and an elastic layer forming material for reinforcing asteel structure, a reinforcing effect by the fiber sheet is preventedfrom being eliminated by sunlight irradiation or the like, a sufficientreinforcing effect can be obtained, and the fiber sheet is preventedfrom being peeled away from the steel structure surface before the fibersheet is broken.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an example of a reinforced steel structureto explain a reinforcing method and a reinforcing structure for a steelstructure according to the present invention.

FIG. 2 illustrates an embodiment of a fiber sheet that can be used inthe reinforcing method for a steel structure according to the presentinvention.

FIG. 3 illustrates another embodiment of the fiber sheet that can beused in the reinforcing method for a steel structure according to thepresent invention.

FIG. 4 is a perspective view showing an embodiment of the fiber sheetthat can be used in the reinforcing method for a steel structureaccording to the present invention.

FIGS. 5( a) and (b) illustrate in section examples of a fiber-reinforcedplastic strand configuring the fiber sheet that can be used in thereinforcing method for a steel structure according to the presentinvention.

FIGS. 6( a) and (b) illustrate in section other embodiments of the fibersheet that can be used in the reinforcing method for a steel structureaccording to the present invention.

FIGS. 7( a) to (f) illustrate working steps for explaining an embodimentof the reinforcing method for a steel structure according to the presentinvention.

FIG. 8 illustrates working steps for explaining another embodiment ofthe reinforcing method for a steel structure according to the presentinvention.

FIG. 9 illustrates a configuration of a bending strength test apparatusto verify the reinforcing method for a steel structure according to thepresent invention.

FIG. 10 is a graph showing a bending test result of a steel structurereinforced according to the present invention.

FIG. 11 is a graph showing a bending test result of a reinforced steelstructure to compare the present invention with comparative examples.

FIG. 12 is a graph showing a bending test result of a reinforced steelstructure to compare the present invention with comparative examples.

EMBODIMENT FOR CARRYING OUT THE INVENTION

A reinforcing method and a reinforcing structure for a steel structureand an elastic layer forming material for reinforcing a steel structureaccording to the present invention will be described in more detail withreference to the accompanying drawings.

Referring to FIG. 1, according to the reinforcing method for a steelstructure according to the present invention, a fiber sheet 1 containingcontinuous reinforcing fibers f is bonded to the surface of a steelstructure 100 through an elastic layer 104 to integrate the steelstructure 100 and the fiber sheet 1 with each other.

The characteristics of the reinforcing method for a steel structureaccording to the present invention resides in the constructioncomprising the steps of:

(a) applying a polyurea resin putty to the surface 102 of the steelstructure 100 and harden the polyurea resin putty to form the elasticlayer 104 as a buffer layer; and

(b) bonding the fiber sheet 1 to the surface of the steel structure 100having the elastic layer 104 formed thereon by using an adhesive agent105 the glass transition temperature of which is adjusted to 60° C. ormore as needed.

More specifically, according to the present invention, there is provideda reinforcing structure for a steel structure characterized byincluding:

(a) an elastic layer 104 formed by applying a polyurea resin putty onthe surface 102 of the steel structure 100; and

(b) a fiber sheet layer 106 bonded to the surface 102 of the steelstructure 100 having the elastic layer 104 formed thereon with theadhesive agent 105 and impregnated with a resin. The elastic layer 104has a tensile elongation of 400% or more in hardening, a tensilestrength of 8 N/mm² or more, and a tensile elastic modulus of 60 N/mm²or more and 500 N/mm² or less.

According to the present invention, preferably, before the elastic layer104 is formed on the surface of the steel structure 100, surfacepreparation can be performed to the surface 102 of the steel structure1. Furthermore, a primer is applied to the steel structure surface 102.

Materials used in the present invention will be described below.

(Fiber Sheet)

In the present invention, the fiber sheets 1 in various forms can beused. An example of the fiber sheet 1 is concretely explained asConcrete Examples 1 to 3. The forms of the fiber sheets 1 used in thepresent invention are not limited to the fiber sheets of the concreteexamples.

CONCRETE EXAMPLE 1

FIG. 2 shows an example of the fiber sheet 1 that can be used in thepresent invention. As the fiber sheet 1, there is used a fiber sheet 1Awhich is not impregnated with a resin and in which continuousreinforcing fibers f are arranged in one direction and configured in theform of a sheet.

More specifically, the fiber sheet 1A can be configured such that areinforcing fiber sheet including the continuous reinforcing fibers farranged in one direction is held by a strand fixing member 3 that is amesh like support sheet or the like. For example, when carbon fibers areused as the reinforcing fibers f, for example, a plurality ofresin-unimpregnated single fiber bundles obtained by bundling 6000 to24000 single fibers (carbon fiber monofilaments) f each having anaverage diameter of 7 μm are used and arranged in one direction inparallel with each other. A fiber weight of the carbon fiber sheet 1A isusually set to 30 to 1000 g/m².

A thermoplastic resin of a low-melting-point type is impregnated in thesurfaces of weft threads 4 and warp threads 5 configuring the mesh-likesupport sheet serving as the strand fixing member 3. The mesh-likesupport sheet 3 is laminated on one surface or both surfaces of carbonfibers arranged in the form of a sheet and heated and pressed to weldportions of the weft threads 4 and the warp threads 5 of the mesh-likesupport sheet 3 to the carbon-fiber sheet.

The mesh-like support sheet 3 is not limited to the two-axesconfiguration. The mesh-like support sheet 3 can also be formed byarranging glass fibers along three-axes or arranging glass fibers asonly the warp threads 5 perpendicular to carbon fibers arranged in onedirection, i.e., along one axis, and bonded to the sheet-like carbonfibers.

As a line of thread of the strand fixing member 3, for example, acompound fiber having a double structure having a glass fiber as a corethereof and a low-melting-point thermo-fusing polyester arranged aroundthe glass fiber is also preferably used.

CONCRETE EXAMPLE 2

As the fiber sheet 1, as shown in FIG. 3, there can also be used a fibersheet (so-called FRP plate) 1B obtained by impregnating a resin Re in areinforcing fiber sheet in which the plurality of reinforcing fibers fare arranged in one direction, for example, the fiber sheet 1A as shownin FIG. 2 and hardening the resin.

In the fiber sheets 1A and 1B described in Concrete Examples 1 and 2described above, as the reinforcing fibers f, not only carbon fibers butalso glass fibers, basalt fibers; metal fibers such as boron fibers,titanium fibers, steel fibers; and, furthermore, organic fibers such asaramid fibers, PBO (Poly(p-phenylenebenzobisoxazole)) fibers, polyamidefibers, polyarylate fibers, and polyester fibers are singly used or usedby mixture as hybrid fibers.

As the resin Re in the fiber sheet 1B according to Concrete Example 2, athermosetting resin or a thermoplastic resin can be used. As thethermosetting resin, a room-temperature-setting or thermosetting epoxyresin, a vinylester resin, an MMA resin, an acrylic resin, anunsaturated polyester resin, a phenol resin, or the like is preferablyused. As the thermoplastic resin, nylon, vinylon, or the like can bepreferably used. An amount of impregnated resin is set to 30 to 70% byweight, more preferably, 40 to 60% by weight.

CONCRETE EXAMPLE 3

Furthermore, as shown in FIGS. 4 and 5, as the fiber sheet 1, a fibersheet 1C in which a plurality of continuous fiber-reinforced plasticstrands 2 impregnated with a matrix resin R and hardened and each havinga small diameter are arranged in the longitudinal direction in the formof a blind, and are fixed to each other with the strand fixing member 3can also be used.

The fiber-reinforced plastic strands 2 can have an almost circularsectional shape (FIG. 5( a)) having a diameter (d) of 0.5 to 3 mm or analmost rectangular sectional shape (FIG. 5( b)) having a width (w) of 1to 10 mm and a thickness (t) of 0.1 to 2 mm. As a matter of course, asneeded, other various sectional shapes may be used.

As described above, in the fiber sheet 1 arranged in one direction inthe form of a blind, the strands 2 are closely spaced apart from eachother with gaps (g)=0.05 to 3.0 mm are fixed with the strand fixingmember 3. A length (L) and a width (W) of the fiber sheet 1 formed asdescribed above are arbitrarily determined depending on the dimensionsand shape of a structure to be reinforced. However, in terms ofhandling, in general, an overall width (W) is set to 100 to 1000 mm. Astrip-like sheet having a length (L) of about 1 to 5 m or a sheet havinga length (L) of 100 m or more can be manufactured. However, the sheet isarbitrarily cut and used.

The fiber sheet 1C can also be manufactured such that the length (L) isset to about 1 to 5 m and the width W is set to about 1 to 10 m largerthan the length (L).

Also in the fiber sheet 1C, as the reinforcing fibers f, carbon fibers,glass fibers, basalt fibers; metal fibers such as boron fibers, titaniumfibers, and steel fibers; and, furthermore, organic fibers such asaramid fibers, PBO (Poly(p-phenylenebenzobisoxazole)) fibers, polyamidefibers, polyarylate fibers, and polyester fibers are singly used or usedby mixture as hybrid fibers. As the matrix resin R impregnated in thefiber-reinforced plastic strand 2, a thermosetting resin or athermoplastic resin can be used. As the thermosetting resin, aroom-temperature-setting or thermosetting epoxy resin, a vinylesterresin, an MMA resin, an acrylic resin, an unsaturated polyester resin, aphenol resin, or the like is preferably used. As the thermoplasticresin, nylon, vinylon, or the like can be preferably used. An amount ofimpregnated resin is set to 30 to 70% by weight, more preferably, 40 to60% by weight.

As a method of fixing the strands 2 with the strand fixing member 3, asshown in FIG. 4, for example, there can be employed a method in whichweft threads are used as the strand fixing member 3 and in which theweft threads are put into the strands in the form of a sheet-like shapeconfigured by the plurality of strands 2 arranged in one direction inthe form of a blind, i.e., a continuous strand sheet, at predeterminedintervals (P) perpendicular to the strands so as to be woven. Theintervals (P) for putting the weft threads 3 are not limited. However,the intervals are selected within a range of intervals usually from 10to 100 mm in consideration of handling properties of the manufacturedfiber sheet 1.

At this time, the weft threads 3 are a line of threads obtained bybundling a plurality of glass fibers or organic fibers each having, forexample, a diameter of 2 to 50 μm. As the organic fibers, nylon,vinylon, or the like is preferably used.

As another method of fixing the strands 2 in the form of a blind, asshown in FIG. 6( a), a mesh-like support sheet can be used as the strandfixing member 3.

More specifically, a configuration in which one surface or both surfacesof the plurality of strands 2 arranged in the form of a blind and havinga sheet-like shape, i.e., a strand sheet is supported with the mesh-likesupport sheet 3 that is manufactured with glass fibers or organic fiberseach having a diameter of, for example, 2 to 50 μm and has the sameconfiguration as described in Concrete Example 1 can be used.

Furthermore, as another method of fixing the strands 2 in the form of ablind, as shown in FIG. 6( b), as the strand fixing member 3, forexample, a flexible belt-like member that is an adhesive tape, a stickytape, or the like can be used. The flexible belt-like member 3 isattached to one surface or both the surfaces of the plurality offiber-reinforced plastic strands 2 in a direction perpendicular to thelongitudinal direction of each of the fiber-reinforced plastic strands 2arranged in the form of a blind and having a sheet-like shape to fix thefiber-reinforced plastic strands 2.

More specifically, as the flexible belt-like member 3, an adhesive tapeor a sticky tape such as a polyvinyl chloride tape, a paper tape, acloth tape, or a nonwoven tape each having a width (w1) of about 2 to 30mm is used. The tapes 3 are generally attached to the fiber-reinforcedplastic strands 2 at intervals (P) of 10 to 100 mm in a directionperpendicular to the longitudinal direction of each of thefiber-reinforced plastic strands 2.

Furthermore, the flexible belt-like member 3 can also be achieved suchthat a thermoplastic resin such as nylon or an EVA resin is fused in theform of a belt on one surface or both the surfaces of the strands 2 in adirection perpendicular to the longitudinal direction of the strands 2.

(Reinforcing Method)

A reinforcing method for a steel structure will be described below withreference to FIG. 7. According to the present invention, a steelstructure is reinforced by using the fiber sheet 1 manufactured asdescribed above.

More specifically, according to the reinforcing method for a steelstructure of the present invention, for example, as the fiber sheet 1,the fiber sheet 1A described in Concrete Example 1 and manufactured byarranging the reinforcing fibers f in one direction can be used. Thefiber sheet 1A is caused to adhere onto the elastic layer 104 formed onthe surface of the steel structure with the adhesive agent 105 tointegrate the elastic layer 104 with the fiber sheet 1A. At this time,while the fiber sheet 1A is caused to adhere to the steel structure,impregnation of the fiber sheet 1A with an adhesive agent (matrix resin)can also be performed by the adhesive agent.

In this manner, there is formed a reinforcing structure 200 for a steelstructure having the elastic layer 104 and the fiber sheet layer 106 onwhich the fiber sheet 1 is impregnated with a resin.

In reinforcement of the steel structure 100, the fiber sheet 1 is bondedto a member (structure) that mainly receives a bending moment and axialforce such that an orientation direction of reinforcing fibers is almostmatched with a main stress direction of tensile stress or compressionstress generated by the bending moment, so that the fiber sheet 1 iseffectively loaded with stress to make it possible to efficientlyincrease a load-carrying capacity of the structure.

When the bending moment acts in two orthogonal directions, the fibersheets 1 of two or more layers are orthogonally laminated and caused toadhere to each other such that an orientation direction of thereinforcing fibers f of the fiber sheets 1 is almost matched with mainstress generated by the bending moment to make it possible toefficiently increase a load-carrying capacity.

(First Step)

As shown in FIGS. 7( a) and 7(b), as needed, a weak portion 101 a of areinforced surface (i.e., a bonded surface) 101 of the steel structure100 is removed with a polishing means 50 such as a disk sander, asandblast, a steel shot blast, or a water jet to perform surfacepreparation on the adhesive surface 101 of the steel structure 100.

(Second Step)

An epoxy modified urethane resin primer 103 is applied to the surface102 subjected to surface preparation (FIG. 7( c)). As the primer 103 isnot limited to epoxy modified urethane resins. An MMA resin or the likeis arbitrary selected in accordance with the materials of the elasticlayer 104 (FIG. 7( d)) and the reinforced steel structure 100.

The step of applying the primer 103 can also be omitted.

(Third Step)

The polyurea resin putty 104 is applied to the surface 102 subjected tosurface preparation to have a desired thickness (T) and hardened to formthe elastic layer 104 (FIG. 7( d)). The application thickness (T) isarbitrarily set in accordance with an uneven surface of the bondedsurface 102 and the thickness T of the fiber sheet 1. However, ingeneral, T=about 0.2 to 10 mm is given.

In the present invention, the polyurea resin putty having a low elasticmodulus, i.e., a material forming the elastic layer 104 (elastic layerforming material) contains a main resin, a hardening agent, a filler, anadditive agent, and the like and has a composition. An example of thecomposition is as follows.

(i) The main resin: a prepolymer containing isocyanate (for example, 4,4′ diphenylmethane diisocyanate) as a reactive component and havingresidual terminal isocyanate the NCO weight percent of which is adjustedto 1 to 16 parts by weight is used.

(ii) The hardening agent: a hardening agent containing an aromatic amine(for example, amine equivalent of 80 to 90) as a main component is used,an equivalence ratio of NCO serving as a main resin to an amine beinggiven by 1.0:0.55 to 0.99 parts by weight. Furthermore, the hardeningagent can contain p-toluenesulfonate or the like as a hardeningaccelerator.

(iii) The filler: a filler contains silica powders, a thixotropic agent,and the like, the components being arbitrarily combined with each otherat 1 to 500 parts by weight.

(iv) The additive agent: an additive agent contains a coloring agent, aviscosity modifier, an elasticizer, and the like, the components beingarbitrarily combined with each other at 1 to 50 parts by weight. Thepolyurea resin putty has a tensile elongation of 400% or more aftercuring (in a normal state, 400 to 600%), a tensile strength of 8 N/mm²or more (in a normal state, 8 to 10 N/mm²), and a tensile elasticmodulus of 60 N/mm² or more and 500 N/mm² or less (in a normal state, 60to 100 N/mm²).

When the elastic modulus is less than 60 N/mm², necessary reinforcingstress cannot be transmitted. In contrast to this, when the elasticmodulus exceeds 100 N/mm², especially, 500 N/mm², extensibility isdisadvantageously short.

In order to use the polyurea resin as a putty, a viscosity obtained at arotating speed of 2 by a BM viscometer is 200 to 700 Pa·s at 23° C., andfalls within the range of 60 to 100 Pa·s at a rotating speed of 20. Athixotropic index, i.e., a ratio of measurement values of viscositiesobtained at different rotating speeds by a rotational viscometer((viscosity at a rotating speed of 20)/(viscosity at a rotating speed of2)) is desirably 4 to 7.

More specifically, when the viscosity is smaller than 60 Pa·s and thethixotropic index is smaller than 4, sag down or the like occurs afterthe application to make smoothing of applied surfaces and application ofa ceiling plane and a wall surface difficult. In contrast to this, whenthe viscosity is larger than 100 Pa·s and the thixotropic index exceeds7, the resin is hard and poses a problem in mixing, and the resin cannotbe easily smoothly applied.

In this case, the following Table 1 shows results obtained by comparingthe physical properties of an epoxy resin putty conventionally used as amaterial forming a buffer layer described in Patent Document 1 and thepolyurea resin putty having the above composition and serving as amaterial forming the elastic layer used in the present invention.

TABLE 1 Conventional technique Present invention Remarks Tensileelongation 100-200% 423% Considerably of buffer layer deviated Tensilestrength of 0.1-50 N/mm² 8.04 N/mm² Conformable buffer layer Tensileelastic 0.1-50 N/mm² 61.3 N/mm² Deviated modulus of buffer layer Amountof filler 0 to 50% by mass 33.1% by mass Conformable Application100-2000 μm 1000 μm Conformable thickness regulation

TABLE 2 Relationship between temperature and tensile elastic modulus ofbuffer layer Test temperature Conventional technique Present invention−20° C. 1600 N/mm² 99.2 N/mm²  0° C. 1500 N/mm² 85.1 N/mm²  23° C.  100N/mm² 61.3 N/mm²  40° C.  12 N/mm² 61.0 N/mm²  60° C.  12 N/mm² 61.0N/mm²

According to the results of Table 1 and the table (Table 2) of therelation between the temperature and the elastic modulus of the bufferlayer, when the epoxy resin putty is used, elongation and toughnesscannot be compatible. In particular, at a high temperature, the materialstrength of the epoxy resin is deteriorated to make it impossible toexert a steel reinforcing effect. In addition, at a low temperature inwinter, the enlargement property is extremely deteriorated to hard theresin so as to cause early peeling.

In contrast to this, the polyurea resin putty used in the presentinvention can exert stable performance at a temperature of −20° C. to+70° C. Thus, the polyurea putty is used as an elastic layer formingmaterial for reinforcing a steel structure and can achieve prevention ofpeeling and a repairing/reinforcing effect can be achieved regardless ofa change in temperature. It is understood that the polyurea resin puttycan be very preferably used in the method of reinforcing a steelstructure.

(Fourth Step)

As shown in FIGS. 7( e) and 7(f), when the resin putty is hardened toform the elastic layer 104, the adhesive agent 105 is applied to theelastic layer 104. The fiber sheet 1 is pressed against the surface ofthe adhesive agent 105 to bond the fiber sheet 1 to the surface 102 ofthe concrete structure 100 to be reinforced through the elastic layer104.

As the adhesive agent 105, in order to apply the adhesive agent 105 at ahigh temperature, preferably, an adhesive agent having a glasstransition temperature adjusted to 60° C. or more, normally, 70° C. to100° C. is used. As described above, the steel structure 100, i.e., asteel product has a surface temperature that increases to about 60° C.by direct sunlight in summer in this country. For this reason, anadhesive agent used in reinforcement by a fiber sheet having aconventional specification softens at this temperature. It is understoodthat a necessary repairing/reinforcing effect cannot be obtained in somecases.

Thus, when an adhesive agent having a glass transition temperature of,preferably 60° C. or more, normally, 70° C. to 100° C. is used as theadhesive agent 105, a reinforcing effect can be prevented from beingeliminated by direct sunlight, and a sufficient reinforcing effect canbe obtained. In addition, the fiber sheet can be prevented from beingpeeled away from the steel structure surface before the fiber sheet isbroken.

As an adhesive agent having the above characteristics, aroom-temperature-setting epoxy resin, an epoxy acrylate resin, anacrylic resin, an MMA resin, a vinylester resin, an unsaturatedpolyester resin, or a UV curable resin is given. More specifically, theroom-temperature-setting epoxy resin and the MMA resin are preferablyused.

In the embodiment, an epoxy resin adhesive agent is used. The epoxyresin adhesive agent is provided as two components including a mainresin and a hardening agent. An example of the composition of the epoxyresin adhesive agent is as follows.

(i) The main agent: a main resin containing an epoxy resin as a maincomponent and a silane coupling agent serving as an adhesion enhancingagent as needed is used. As the epoxy resin, for example, a bisphenolepoxy resin, in particular, a rubber modified epoxy resin to givetoughness can be used. Furthermore, a reactive diluent and a thixotropicagent may be added as usage.

(ii) The hardening agent: a hardening agent contains amines as maincomponents, a hardening accelerator as needed, a coloring agent, and thelike is used as an additive agent. An equivalence ratio of an epoxyresin serving as the main resin to amines of the hardening agent is 1:1.As the amines, for example, an aliphatic amine containingmetaxylenediamine and isophoronediamine can be used. The epoxy resinhaving the above composition has a glass transition temperature of 70°C. or more (74° C.).

In the above description, the adhesive agent 105 is applied onto theelastic layer 104. However, as a matter of course, the adhesive agent105 can also be applied to the fiber sheet 1 or may be applied onto bothof the surface of the elastic layer 104 and the bonded surface of thefiber sheet 1.

When quantity of reinforcement is large, a plurality of fiber sheets 1can be bonded to adhere to the surface of the structure. However, whenthe plurality of fiber sheets 1 are laminated and bonded to adhere toeach other, stress may be concentrated on an end portion, and resistanceto peeling/breaking may be lowered.

Thus, in order to prevent the sheet from being peeled and broken, asshown in FIG. 8, sheet lengths (L) (see FIG. 1) of the fiber sheets 1 ofthe respective layers are preferably changed. For example, the lengthsof the fiber sheets 1 laminated as a plurality of layers are graduallydecreased toward an outer layer spaced apart from the structure surface102, and end portions la of the fiber sheets 1 are stepwise laminated.Shift lengths (h) of the sheet end portions la are properly set to about30 mm to 300 mm. For example, the sheets 1 are bonded to each other togradually decrease the lengths of the sheet end portions 1 a by 100 mmeach to make it possible to obtain a preferable effect.

More specifically, the end portions la are stepwise laminated such thatthe lengths (L) of the fiber sheets 1 laminated as a plurality of layersare gradually reduced toward the outer layer by about 30 to 300 mm tomake it possible to reduce stress concentration on the sheet endportions la and to improve the resistance to peeling.

The following experiments were executed to prove the operationaladvantages of the reinforcing method and the reinforcing structure of astructure and an elastic layer forming material for reinforcing a steelstructure according to the present invention.

EXPERIMENTAL EXAMPLE 1

In this experimental example, the fiber sheet 1 was used to reinforce asteel plate serving as the steel structure 100 according to an adhesionmethod. The fiber sheet 1 used in the experimental example was the fibersheet 1A having the configuration described as Concrete Example 1 withreference to FIG. 2.

As the reinforcing fibers f in the fiber sheet 1A, resin-unimprgnatedpitch-based carbon fiber strands including 6000 fibers as bundled, eachhaving an average diameter of 10 μm were arranged in one direction inthe form of a sheet such that a fiber weight is 300 g/m². The 2-axismesh-like support member 3 manufactured by using glass fibers wasadhered on one surface of the sheet-like reinforcing fibers to form thefiber sheet 1A.

The fiber sheet 1 serving as the fiber sheet 1A manufactured asdescribed above had a width (W) of 500 mm and a length (L) of 50 m. Inthe embodiment, the fiber sheet is arbitrarily cut and used.

As described below, the steel plate 100 serving as a steel structure wasreinforced by the same fiber sheet adhering method as described abovewith reference to FIG. 7 by using the fiber sheet 1. In the experiment,it is assumed that the fiber sheet 1 is attached to the lower surface ofthe steel plate 100.

In the experimental example, the lower surface of the steel product 100was ground and cleaned by shotblasting to obtain a rough surface. Anepoxy modified urethane primer (“FORCAUL-1” (tradename) available fromNippon Steel Materials CO., LTD.) 103 was applied to the surface 102 ofthe steel plate 100 at 0.15 kg/m².

After the epoxy modified urethane resin primer 103 was dried to thetouch, in order to form the elastic layer 104 in the situation where theapplied surface is a overhung surface, the polyurea resin putty havingthe composition described above was applied to the steel plate(specimen) 100 with a knife to have a thickness (T) of 1 mm. At thistime, the polyurea resin putty kept adhering to the steel plate specimen100 without dropping with its own weight after the completion of theapplication.

A viscosity of the putty-like polyurea resin used as the forming resinof the elastic layer 104 obtained at 23° C. and a rotating speed of 2 bya BM viscometer was 600 Pa·s, and a viscosity at a rotating speed of 20was 95 Pa·s.

A thixotropic index ((viscosity at a rotating speed of 20)/(viscosity ata rotating speed of 2)) was 6.32.

The polyurea resin putty applied to the steel product surface 102 washardened to form the elastic layer 104. The epoxy resin having a glasstransition temperature of 74° C. and the composition described above wasapplied to the elastic layer 104 at an application quantity of 0.4 kg/m²(as a base coat on each layer when the plurality of fiber sheets 1 arelaminated). After the fiber sheet 1 was lightly pressed against theepoxy-resin-applied surface, a plastic roller having a width of 100 mmand a diameter of 10 mm was moved on the fiber sheet 1 while beingapplied with a pressure force of about 100 N. As the fiber sheets, atotal of 7 fiber sheets each having the configuration described abovewere laminated with an adhesive agent. More specifically, 5 “carbonfiber sheets C830” (tradename) available from Nippon Steel MaterialsCO., LTD. and 2 “carbon fiber sheets C160 (tradename) available fromNippon Steel Materials Co., LTD. were laminated.

The fiber sheet 1 was pressed from the upper surface of the sheet 1 byrolling a plastic roller, so that the epoxy resin was oozed from thegaps between the fibers of the fiber sheet 1. The fiber sheet wasattached to the steel plate 100 without being held by some means, andwas not peeled away from the steel plate 100.

As in the example, when the plurality of fiber sheets 1 were laminated,the epoxy resin 105 was applied to the surface of each of the fibersheets 1 as a coating at an application quantity of 0.2 kg/m², and thesurface was flatly finished with a rubber knife Thereafter, theresultant structure was cured at room temperature for one week. Thefiber sheet 1 could be very preferably bonded to the steel plate 100without generating voids in the attaching surface of the fiber sheet 1.

The fiber sheet reinforcing steel plate (present invention) 100manufactured as described above and the fiber sheet reinforcing steelplates 100 using an epoxy-resin-impregnated adhesive agent having aglass transition temperature of 48° C. serving as an adhesive agent anda polyurethane resin putty (Comparative Example 1) and a soft epoxyresin putty (Comparative Example 2) as putty were subjected to athree-point bending test at an inter-fulcrum distance Ls of 80 mm byusing a test apparatus shown in FIG. 9. The cross section of each of thesteel plates 100 has a width W0=25 mm, a thickness T0=2.0 mm, and atotal length L0=100 mm. Three specimens, as described above, weremanufactured with the same structures and the same materials expect thatthe adhesive agent 105 and the putty 104 with which the fiber sheetswere caused to adhere to the steel plate surfaces.

Constituent materials of the present invention and Comparative Examples1 and 2 in the experiment are summarized to obtain the following Table3.

TABLE 3 Impregnated Continuous fiber Putty adhesive agent sheet materialPresent Invention Polyurea resin Tg 74° C. epoxy C830 × 5 layers + puttyC160 × 2 layers Comparative Polyurethane resin Tg 48° C. epoxy C830 × 5layers + Example 1 putty C160 × 2 layers Comparative Soft epoxy resin Tg48° C. epoxy C830 × 5 layers + Example 2 putty C160 × 2 layers

Results of the bending test are shown in FIGS. 10 and 11. According to abending test graph shown in FIG. 11 in which a temperature and a loadchange, the following points are noted.

More specifically, in the specification of Comparative Example 1, adecrease in load occurred at about 30° C., and theepoxy-resin-impregnated adhesive agent was softened. On the other hand,by using the property of the epoxy resin hardened at a low temperature,a high load is exhibited at a low temperature. In this situation, therepairing and reinforcing capabilities cannot be satisfied at a hightemperature under the climate condition in Japan.

In the specification of the Comparative Example 2, when the temperatureis low, the soft epoxy resin putty was hardened due to the temperature,and the epoxy resin putty was early peeled before the load increased.This shows that the reinforcement cannot be attained. At a hightemperature, the soft epoxy resin putty was peeled due to an earlymaterial failure of the soft epoxy resin putty.

In contrast to this, it was confirmed that the polyurea resin puttyaccording to the present invention exhibited stable performance at froma low temperature to a high temperature, and that therepairing/reinforcing material and the working process specificationwhich conform to the climate condition in Japan were established.

EXPERIMENTAL EXAMPLE 2

In the experimental example, by using the same fiber sheet 1 asdescribed in Experimental Example 1, a steel plate serving as the steelstructure 100 was reinforced according to the adhesion method.

More specifically, as the fiber sheet reinforcing steel plate (thepresent invention) 100 according to the present invention, the fibersheet 1 manufactured as described above was attached to the steel plate100, as in Experiment 1, by using a urethane modified epoxy resin primerserving as the primer 103, the polyurea resin putty having the abovecomposition and serving as a putty for the elastic layer 104, and theepoxy resin having a glass transition temperature of 74° C. and thecomposition described above and serving as the adhesive agent 105.

In Comparative Example 3, the fiber sheet 1 manufactured as describedabove was attached to the steel plate 100 by using the epoxy resinprimer serving as the primer 103 and the epoxy resin having a glasstransition temperature of 74° C. and the composition described above andserving as the adhesive agent 105 without using a putty for the elasticlayer 104.

In Comparative Example 4, the fiber sheet 1 manufactured as describedabove was attached, as in Experiment 1, to the steel plate 100 by usingan epoxy modified urethane resin primer serving as the primer 103, apolyurea resin putty serving as a putty for the elastic layer 104, andan epoxy resin (“FR-E3P” (tradename) available from Nippon SteelMaterials Co., LTD.) having a glass transition temperature of 48° C. andserving as an adhesive agent.

By using the three specimens manufactured as described above, the samebending test as that in Experimental Example 1 was executed. Testresults are shown in Table 4 and FIG. 12.

TABLE 4 Unit (N) Comparative Present Invention Comparative Example 4Polyurea resin Example 3 Polyurea resin Temperature putty + high-TgHigh-Tg epoxy putty + low-Tg (° C.) epoxy (74° C.) No putty epoxy (48°C.) −20 1200 1206 1268 5 1184 1272 1203 23 1278 1269 1211 30 1270 11361176 40 1454 1243 1134 50 1249 1050 825 60 1392 900 644

According to a bending test graph shown in FIG. 12 in which atemperature and a load change, the following points are understood.

In Comparative Example 3, as in the present invention, although thehigh-Tg epoxy resin adhesive agent having a glass transition temperatureof 74° C. is used, the fiber sheet 1 is attached to the steel plate 100without using a polyurea resin putty. Thus, in comparison with thepresent invention, in Comparative Example 3, the effect of the polyurearesin putty (elastic layer 104) can not been obtained, so thatsufficient reinforcement of the steel plate cannot be achieved with anincrease in temperature. Also in Comparative Example 3, the epoxy resinadhesive agent was finally peeled as in Comparative Example 2.

In Comparative Example 4, the polyurea resin putty was used as in thepresent invention, a relatively-low-Tg epoxy resin adhesive agent havinga glass transition temperature of 48° C. was used as an adhesive agent.As also in the case, although peeling of the fiber sheet layer 106 canbe prevented due to the effect of the polyurea resin putty (elasticlayer 104) as in the present invention, a bending load moderatelydecreases from about a glass transition temperature of 48° C. Incomparison with the present invention, reinforcement itself was notsufficiently achieved at a high temperature. More specifically,Comparative Example 4 shows a situation in which the fiber sheet layer106 using carbon fibers are bent together with the steel plate. Thus,even at a high temperature, in order to obtain a reinforcing effect, theglass transition point of the adhesive agent must be adjusted, and theglass transition point of the adhesive agent must be set to 60° C. ormore, preferably, 70° C. or more for temperature control required forthe climate condition.

In this manner, according to the reinforcing method and a reinforcingstructure for a steel structure and the elastic layer forming materialfor reinforcing a steel structure of the present invention, it wasproved that the steel structure 100 could be effectively reinforced.

REFERENCE NUMERALS

-   1 Fiber sheet-   2 Fiber-reinforced plastic strand-   3 Strand fixing member (weft threads, mesh support sheet, and    flexible belt-like member)-   100 Steel structure-   103 Primer-   104 Elastic layer-   105 Adhesive agent-   106 Fiber sheet layer-   200 Reinforcing structure

1. A reinforcing method for a steel structure in which a fiber sheetincluding reinforcing fibers is bonded to a surface of the steelstructure to integrate the fiber sheet with the steel structure, themethod comprising the steps of: (a) applying a polyurea resin putty tothe surface of the steel structure and hardening the polyurea resinputty to form an elastic layer; and (b) bonding the fiber sheet to thesurface of the steel structure having the elastic layer formed thereonwith an adhesive agent.
 2. The reinforcing method for a steel structureaccording to claim 1, wherein the adhesive agent used in the step (b)has a glass transition temperature adjusted to make it possible tomaintain a reinforcing effect even at a high temperature.
 3. Thereinforcing method for a steel structure according to claim 1, whereinthe adhesive agent has a glass transition temperature of 60° C. or more.4. The reinforcing method for a steel structure according to claim 1,wherein the polyurea resin putty forming the elastic layer in the step(a) contains a main resin, a hardening agent, a filler, and an additiveagent and has a composition containing: (i) the main resin: a prepolymercontaining an isocyanate as a reactive component and having residualterminal isocyanate the NCO weight percent of which is adjusted to 1 to16 parts by weight is used; (ii) the hardening agent: a hardening agentcontaining an aromatic amine as a main component is used, an equivalenceratio of NCO serving as the main resin to an amine being given by1.0:0.55 to 0.99 parts by weight; (iii) the filler: a filler containssilica powders, a thixotropic agent, and the like, and is arbitrarilycompounded at 1 to 500 parts by weight; and (iv) the additive agent: anadditive agent contains a coloring agent, a viscosity modifier, anelasticizer, and the like, and is arbitrarily compounded at 1 to 50parts by weight.
 5. The reinforcing method for a steel structureaccording to claim 1, wherein the adhesive agent used in the step (b) isa room-temperature-setting epoxy resin, an epoxy acrylate resin, anacrylic resin, an MMA resin, a vinylester resin, an unsaturatedpolyester resin, or a UV curable resin.
 6. The reinforcing method for asteel structure according to claim 5, wherein the adhesive agent is anepoxy resin adhesive agent, and the epoxy resin adhesive agent isprovided by two components including a main resin and a hardening agent,and has a composition containing: (i) the main agent: a main resincontaining an epoxy resin as a main component and a silane couplingagent or the like serving as an adhesion enhancing agent as needed isused; and (ii) the hardening agent: a hardening agent contains amines asmain components, an equivalence ratio of an epoxy resin serving as themain resin to amines of the hardening agent being 1:1.
 7. Thereinforcing method for a steel structure according to claim 1, whereinprior to forming the elastic layer on the surface of the steelstructure, the method includes performing surface preparation to thesurface of the steel structure and/or applying a primer.
 8. Thereinforcing method for a steel structure according to claim 1, whereinthe fiber sheet is a fiber sheet in which continuous reinforcing fibersarranged in one direction are fixed to each other with a strand fixingmember.
 9. The reinforcing method for a steel structure according toclaim 1, wherein the fiber sheet is a fiber sheet in which a pluralityof continuous fiber-reinforced plastic strands each formed byimpregnating the matrix resin in the reinforcing fibers and hardeningthe resin, are arranged in a longitudinal direction in the form of ablind and fixed to each other with a strand fixing member.
 10. Thereinforcing method for a steel structure according to claim 1, whereinthe fiber sheet is a fiber sheet in which a resin is impregnated incontinuous reinforcing fiber sheets arranged in one direction andhardened.
 11. The reinforcing method for a steel structure according toclaim 1, wherein the plurality of fiber sheets are laminated on asurface of the steel structure, bonded to the surface, and integratedwith the steel structure.
 12. An elastic layer forming material forreinforcing a steel structure that includes a polyurea resin pattyforming the elastic layer in the reinforcing method for a steelstructure according to claim 1, wherein the polyurea resin puttycontains a main resin, a hardening agent, a filler, and an additiveagent and has a composition containing: (i) the main resin: a prepolymercontaining an isocyanate as a reactive component and having residualterminal isocyanate the NCO weight percent of which is adjusted to 1 to16 parts by weight is used; (ii) the hardening agent: a hardening agentcontaining an aromatic amine as a main component is used, an equivalenceratio of NCO serving as the main resin to an amine being given by1.0:0.55 to 0.99 parts by weight; (iii) the filler: a filler containssilica powders, a thixotropic agent, and the like, and is arbitrarilycomposed at 1 to 500 parts by weight; and (iv) the additive agent: anadditive agent contains a coloring agent, a viscosity modifier, anelasticizer, and the like, and is arbitrarily compounded at 1 to 50parts by weight.
 13. The elastic layer forming material for reinforcinga steel structure according to claim 12, wherein the polyurea resinputty has a tensile elongation of 400% or more after curing, a tensilestrength of 8 N/mm² or more, and a tensile elasticity modulus of 60N/mm² or more and 500 N/mm² or less.
 14. A reinforcing structure for asteel structure that reinforces the steel structure, comprising: (a) anelastic layer formed by applying a polyurea resin putty on a surface ofthe steel structure; and (b) a fiber sheet layer bounded to the surfaceof the steel structure having the elastic layer formed thereon with anadhesive agent and impregnated with a resin.
 15. The reinforcingstructure for a steel structure according to claim 14, wherein theelastic layer has a tensile elongation of 400% or more in hardening, atensile strength of 8 N/mm² or more, and a tensile elasticity modulus of60 N/mm² or more and 500 N/mm² or less.
 16. The reinforcing structurefor a steel structure according to claim 14, wherein the adhesive agenthas a glass transition temperature that is adjusted such that areinforcing effect can also be maintained even at a high temperature.17. The reinforcing structure for a steel structure according to claim14, wherein the adhesive agent has a glass transition temperature thatis adjusted such that a reinforcing effect can also be maintained evenat a high temperature.
 18. The reinforcing structure for a steelstructure according to claim 14, wherein the polyurea resin puttycontains a main resin, a hardening agent, a filler, and an additiveagent and has a composition containing: (i) the main resin: a prepolymercontaining an isocyanate as a reactive component and having residualterminal isocyanate the NCO weight percent of which is adjusted to 1 to16 parts by weight is used; (ii) the hardening agent: a hardening agentcontaining an aromatic amine as a main component is used, an equivalenceratio of NCO serving as a main resin to an amine being given by 1.0:0.55to 0.99 parts by weight; (iii) the filler: a filler contains silicapowders, a thixotropic agent, and the like, and is arbitrarilycompounded at 1 to 500 parts by weight; and (iv) the additive agent: anadditive agent contains a coloring agent, a viscosity modifier, anelasticizer, and the like, and is arbitrarily compounded at 1 to 50parts by weight.
 19. The reinforcing structure for a steel structureaccording to claim 14, wherein the adhesive agent is aroom-temperature-setting epoxy resin, an epoxy acrylate resin, anacrylic resin, an MMA resin, a vinylester resin, an unsaturatedpolyester resin, or a UV curable resin.
 20. The reinforcing structurefor a steel structure according to claim 19, wherein the adhesive agentis an epoxy resin adhesive agent, and the epoxy resin adhesive agent isprovided by two components including a main resin and a hardening agent,and has a component containing: (i) the main agent: a main resincontaining an epoxy resin as a main component and a silane couplingagent or the like serving as an adhesion enhancing agent as needed isused; and (ii) the hardening agent: a hardening agent contains amines asmain components, an equivalence ratio of an epoxy resin serving as themain resin to amines of the hardening agent being 1:1.